I bought a Nidia GTX 650 Ti SSC just after christmas time, I had it in my computer, it was mounted properly, it had the right cables connected and everything was working, After a week of it working I turned it off one night and the next day I tried turning it on it had completely stopped working. I tried it in my friends computer and it did not work at all. I wasn't playing any intense games that would cause it to act up. I brought it back to the shop and they replaced it under the warranty. I had the replaced one which was also brand new put back into my computer it was all working again for about a week again, I turned my computer off how I usually do by shutdown then turning off the mains switch once the shutdown is complete, and in the morning my graphics card wasn't working at all again, it was the exact same problem as I had before. Although I know the shop won't replace it again, i'm just curious as to what could cause it to just randomly stop working. No it has not overheated and it's completely clean with next to nothing dust in it, the pci port is also clean, I have no idea what cause this since I don't know too much about computers, and right now I'm just curious to see what you guys could think that caused this. It came as SSC = SuperSuperClocked as it was purchased.

My PSU is an ACE 500w and I thought if the product is broken and replaced it voids the warranty.

If that's what the shop told you then they are running a scam, especially if the card they replaced it with was brand new as well. Sounds to me like either the card they used wasn't brand new or they are just trying to get out of replacing it, although most places have you return it to the manufacturer unless you pay extra for in-store replacement like best buy or something. Worst case scenario, go to the card manufacturers website, start their rma process, it will ask you to put in the serial number and will tell you whether or not its still under warranty

if so, it doesn't look good, those are very low values for a 500W psu I'm afraid. a good 500W psu should be pushing around 40A on the +12, that one is lucky if it's pushing 20A. no wonder it costs £11, it's utter garbage.

No you dont, just undo the cables and remove the psu. Maybe you should take pictures of the cables and connectors to know where it all goes if you arent good with that, but it should only take you 15 mins